1. Field of the Invention
The present invention generally relates to bar code indicia evaluation systems. More particularly, the invention relates to methods of calibrating indicia evaluation systems having one or more scanner units.
2. Description of the Prior Art
The desire and need to verify bar code symbols is well known in the art. With the ubiquitous bar code symbol now used by virtually all inventory intensive establishments, such as warehouses, wholesale and retail stores, and the like, flexible apparatus are needed to evaluate and verify the quality of various types of bar code symbols.
Bar code indicia evaluation and verification systems currently available may be categorized into two fundamental groups: contact verifiers and non-contact verifiers. Contact verifiers are physically placed in contact with the substrate on which the symbol is printed or otherwise disposed. Non-contact verifiers are often moving beam scanner based units, which may be arranged to scan a succession of bar codes being printed, for example on a high speed printing press. For several reasons, the calibration of contact type scanner units is more straight forward than the calibration of non-contact scanners. First, the distance between a target indicia and the scan head of a contact-type verifier is fixed and known. In addition, ambient light can have a significant affect on the calibration of non-contact verifiers and must be considered when checking and adjusting the calibration of these systems. Generally, contact type verifiers will minimize the affect of ambient light by way of a "hood" or "shroud" that blocks ambient light from illuminating an indicia being scanned during evaluation. Further, contact type verifiers are generally operative to evaluate a single bar code indicia, and are manually positioned to scan the indicia.
To further complicate the evaluation of bar code indicia, a number of rigorous standards have been established in recent years. The purpose of such standards is to establish "quality" requirements and associated verification criteria for various commonly utilized bar code symbologies. The guidelines are established and administered by groups such as the Uniform Code Council (UCC) and the American National Standards Institute (ANSI). The ANSI guideline (X3.182-1990) titled "Bar Code Print Quality Guideline", which was published in 1990, has been accepted as an industry standard and has resulted in a new generation of evaluation equipment that perform "ANSI level verification".
One requirement called for by the various guidelines and standards, including the ANSI guideline, is the requirement that a specified scanning aperture or spot size must be generated by a scanner unit when evaluating different symbologies. (It should be noted that the terms "aperture" and "spot size" are to considered equivalent terms as used in the context of this disclosure.) For instance, the UCC specification titled "Quality Specification for the UPC Printed Symbol", which was published in September 1994, calls for a 6 mil scanning aperture. In contrast, "The Application Standard for Shipping Container Codes", also published by the UCC, calls for a 20 mil aperture. Further, in the absence of an overriding application standard, the ANSI guideline recommends the scanning aperture be selected based on the "density", or equivalently the width "X" of the narrowest element of the indicia to be examined. Table 1, shown below, summarizes the ANSI aperture (spot size) requirements.
TABLE 1 ______________________________________ ANSI Evaluation Aperture Diameters Nominal X Dimension (in Aperture Diameter mils) (in mils) ______________________________________ 4 &lt;= X &lt; 7 3 7 &lt;= X &lt; 13 5 13 &lt;= X &lt; 25 10 25 &lt;= X 20 ______________________________________
It may be noted that X is used to describe the "nominal width", or the "intended width", of the narrowest element of a bar code indicia. Further, the term "density", which is indicative of the amount of data that an indicia can encode in a given unit length, is directly related to the nominal width. As such, the terms density, X, and nominal element width are often used interchangeably.
As a result of the adoption and wide spread acceptance of the above discussed standards and guidelines, there is a need for evaluation systems that may be adjusted (and calibrated) to generate a spot size of a particular diameter. In addition, there is a need for configurable systems, and appropriate methods of calibration, in which an operator may select a particular scanner unit and have it generate a required spot size for the evaluation of a collection of indicia (possibly as a function of the particular symbology or particular X dimension of the elements of the indicia). Further, it would certainly be desirable to provide a system which may generate the required spot size while using the same scanner unit. That is, a system where the scanner unit need not be physically replaced to change from one spot/aperture size to another. As an example, prior art evaluation systems are known that employ a wand as the scanning device. These systems are sold with a plurality of wands that may, one at a time, be operatively coupled to the system. Each wand provides a specific spot size as required for the indicia to be checked. One such system offers at least six different wands that a customer may choose to purchase.
The need to provide on-line high speed verifier equipment is also well known in the art. When considering applications such as a printing press or a high speed conveyor line, there is a need to be able to operatively select and quickly calibrate at least one of a plurality of scanner units. This requirement is driven by the desire to provide on-line verification as indicia are being printed or otherwise disposed on a substrate. As a press may be reconfigured for different print jobs as often as several times a day, those skilled in the art will appreciate the advantage of being able to operatively select and couple one or more particular scanner units for a specific print job. Therefore, there is a need to have systems comprised of a plurality of scanner units, wherein one or more selected scanner units may be operatively coupled to an evaluation unit to analyze the reflectance signals generated by the selected scanner unit(s). An important consideration when employing evaluation systems having the features discussed herein, is to provide simple methods which can be executed by press operators in order to configure and calibrate systems using multiple scanner units and/or scanner units arranged to generate one of a plurality of selectable spot sizes.
It should be noted that moving beam scanning systems are known in the art that utilize techniques to extend the range over which the system can properly scan and decode an indicia. These systems "hunt" for the indicia by sequentially altering the spot size diameter or the distance at which it is focused. Further, there are systems known which can measure the distance between the scanner unit and a target indicia to adjust (optically) the scanning beam. However, such systems are altering the spot size dynamically in order to properly scan and decode an indicia. The actual spot size used that resulted in the scan/decode of the bar code indicia is not of consequence or typically even noted. Further, successive bar code indicia may be scanned with scanning spots of various sizes and not a selected specific spot size wherein the intent is to provide an accurate quantitative evaluation of indicia.
Objects of the present invention are, therefore, to provide new and improved evaluation systems, and associated methods of calibration, having one or more of the following capabilities, features, and characteristics:
the selection of a particular aperture size to be generated by a scanner unit; PA1 the selection, operative coupling, and calibration of at least one scanner unit of a plurality of scanner units available for the evaluation of bar code indicia; PA1 enable the aperture size generated by a scanner unit to be varied by slidably adjusting the distance between the scanner unit and the target indicia; PA1 producing a particular aperture size by adjusting the distance between the scanner unit and the target indicia to produce a measured modulation known to be associated with the particular aperture size; PA1 including an adjustment module to enable the computer controlled (automated) adjustment of the distance between a scanner unit and target indicia to be evaluated; PA1 having computing and evaluation means to enable the automatic adjustment and calibration of one or more scanner units; PA1 the quick and easy adjustment and calibration of at least one of a plurality of scanner units using stored or determined calibration parameter values; and PA1 relatively low cost implementation using primarily off-the-shelf components and devices that are readily available.